Communication system having reduced delay time

ABSTRACT

A communication system includes a transmitter having a signal generator for generating a signal for transmitting data, a transmission delay unit for repeatedly delaying the signal from the signal generator for a predetermined delay time within a symbol period and generating corresponding delayed signals, and a selector for selectively providing one of the delayed signals from the transmission delay unit to an antenna; and a receiver having a reception delay unit for receiving the signal from the transmitter and delaying the signal as long as the delay time of the transmission delay unit, and a data judgment block for discriminating data bits of the signal from the transmitter by comparing the signal from the transmitter with the delayed signal from the reception delay unit. According to the communication system, the delay time can be accurately adjusted even if the delay line is shortened, and the data bits of the communication signal can be accurately judged in the receiver side.

This application claims priority from Korean Patent Application No.2005-114960, filed Nov. 29, 2005 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication system having a reduceddelay time, and more particularly, to a communication system having areduced delay time that can provide an accurate delay time of acommunication signal using a short delay line and that can accuratelyjudge data bits of the communication signal in a receiver.

2. Description of the Related Art

Generally, a spread spectrum communication is a system for spreading asignal to be transmitted so that the signal has a much wider bandwidththan the original signal and transmitting the spread signal, and asystem for transmitting information using a chaotic signal has beenrecently proposed, in accordance with the IEEE 802.15.4a standard.

The chaotic signal modulation system can be designed by a simplehardwired radio frequency (RF) structure, and does not require a circuitsuch as a voltage controlled oscillator (VCO), phase locked loop (PLL),mixer, and so on, which are required in existing RF systems. In the caseof using the chaotic signal modulation system, the power consumption canbe reduced to ⅓ of the power consumption of the conventional system, forexample, to 5 mW.

A differential chaos shift keying (DCSK) system may be arepresentatively used modulation system among various chaotic signalmodulation systems.

The DCSK system has the best bit error rate (BER) characteristic amongthe chaotic signal modulation systems. In the DCSK system that uses areference signal, two chaotic sample parts that correspond to one databit are transmitted for each symbol period. The first sample part isused as the reference signal, and the second sample part is used as adata signal to be transmitted. The second sample part is generated bytransmitting the reference signal as it is or an inverted referencesignal depending on whether a binary symbol being transmitted is “0” or“1”. That is, if the binary symbol is “0”, the second sample part, whichis the data signal, is generated by inverting the reference signal,while if the binary symbol is “1”, the data signal is generated bytransmitting the reference signal as it is. In a receiver side, the databits are extracted by processing correlation between the two receivedsample parts.

FIG. 1 is a block diagram illustrating the construction of aconventional DCSK type communication system. As illustrated in FIG. 1,the communication system includes a transmitter 10 and a receiver 20.

The transmitter 10 includes a chaotic signal generator 11, a multiplier13, a delay unit 15, and a switch 17. The transmitter 10 carries data ona chaotic signal which is transmitted to the receiver 20.

The chaotic signal generator 11 generates the chaotic signal directlyfrom a frequency band for a data transmission.

The multiplier 13 receives the data bits of “0” or “1” for generatingthe data, multiplies the data bits by the chaotic signal generated bythe chaotic signal generator 11, and provides the result ofmultiplication to the delay unit 15. If the data bit is “0”, the chaoticsignal is inverted, and if the data bit is “1”, the chaotic signal ismaintained as it is.

The delay unit 15 generates a data signal, which is included in thelatter half of a symbol period, by delaying the output signal of themultiplier 13 by a half symbol period.

The switch 17 includes a first contact connected to the chaotic signalgenerator 11 and a second contact connected to the delay unit 15, andgenerates a signal to be transmitted to the receiver 20 by selecting oneof the output signals of the chaotic signal generator 11 and the delayunit 15. The switch 17 alternately switches the first and secondcontacts under the control of a control unit (not illustrated), and acontact time is set to ½ of a symbol period Ts.

For example, if the switch 17 is switched to the first contact for ½Ts,the reference signal from the chaotic signal generator 11 is outputthrough the switch. Then, if the switch 17 is switched to the secondcontact, the data signal from the delay unit 15 is output through theswitch 17.

By this switch 17, communication signals as shown in FIGS. 2A and 2B aregenerated. FIG. 2A illustrates a communication signal in the case wherethe reference signal is the same as the data signal, i.e., the data bitis “1”, and FIG. 2B illustrates a communication signal in the case wherethe data signal is the inverted reference signal, i.e., the data bit is“0”.

On the other hand, the receiver 20 includes a delay unit 25, amultiplier 23, a waveform generator 27, and a data judgment unit 29.

The delay unit 25 delays the communication signal input through anantenna as long as the delay time delayed by the delay unit 15 of thetransmitter 10, i.e., for ½Ts. This is to judge the data bits bycomparing the data signal with the reference signal.

The multiplier 23 multiplies the communication signal input through theantenna by a signal delayed through the delay unit 25, and provides theresultant signal to the waveform generator 27. If the reference signaland the data signal are equal to each other, i.e., if the data bit is“1”, a communication signal having twice the energy is output. If thereference signal and the data signal are opposite to each other, i.e.,if the data bit is “0”, a communication signal having twice the negativeenergy is output.

The waveform generator 27 removes the chaotic signal and forms thewaveform of the communication signal by adding the communication signalsoutput from the multiplier 23 for a predetermined period, i.e., for eachsymbol period.

The data judgment unit 29 receives the waveform generated by thewaveform generator 27, and extracts the data bits from the inputwaveform. The data judgment unit 29 judges the data bits depending onwhether the waveform is higher that a predetermined threshold value,which is set to the energy value of “0”. If the waveform is higher thanthe threshold value, the data judgment unit 29 judges the data bit as“1”.I If the waveform is not higher than the threshold value, the datajudgment unit 29 judges the data bit as “0”.

In order to generate the data signal in the conventional DCSK typecommunication system, a long delay line for delaying the signal as longas ½Ts should be provided. In addition, it is not easy to accuratelyperform a delay as long as ½Ts. In the case of comparing the receivedsignal with the delayed signal after the communication signal is delayedas long as ½Ts in the delay unit 25 of the receiver 20, only onecomparison is possible for a symbol period since one reference signaland one data signal exist in a symbol period. Accordingly, if amulti-path reception of a noise or a communication signal occurs, thewaveform output from the waveform generator 27 has an energy value thatis lower than the threshold value although the signal output from thetransmitter 10 is “1”, and this may cause the data bit to be judged as“0”. By contrast, if the waveform output from the waveform generator 27has an energy value that is higher than the threshold value although thesignal output from the transmitter 10 is “0”, the data bit may be judgedas “1”.

Accordingly, a method is needed for not only providing an accurate delaytime of the communication signal through the delay unit 15 but alsoshortening the delay line. In addition, it is required to provide amethod for more accurately judging the data bits for each symbol periodin the receiver side.

SUMMARY OF THE INVENTION

Illustrative, non-limiting embodiments of the present invention overcomethe above disadvantages and other disadvantages not described above.Also, the present invention is not required to overcome thedisadvantages described above, and an illustrative, non-limitingembodiment of the present invention may not overcome any of the problemsdescribed above.

The present invention provides a communication system having a reduceddelay time that can provide an accurate delay time of a communicationsignal using a short delay line and that can reduce the delay time foraccurately judging data bits of the communication signal in a receiver.

According to an aspect of the present invention, there is provided acommunication system having a reduced delay time, which comprises atransmitter that includes a signal generator for generating a signal fortransmitting data, a transmission delay unit for repeatedly delaying thesignal from the signal generator for a predetermined delay time within asymbol period and generating corresponding delayed signals, and aselector for selectively providing one of the delayed signals from thetransmission delay unit to an antenna.

The signal generator may be a chaotic signal generator for generating achaotic signal.

The selector may be a first switch that has a first contact connected tothe signal generator and a second contact connected to the transmissiondelay unit.

The communication system may further include a first multiplier formultiplying the signal generated from the signal generator by a data bitthat is a binary symbol of the data and generating a data signal.

The communication system may further include a delay feedback loop forre-inputting the signal having been delayed through the transmissiondelay unit to the transmission delay unit, and a second multiplier,installed on the delay feedback loop, for multiplying the signal by thesame data bit as that input to the first multiplier.

The communication system may further include a second switch having afirst contact connected to the first multiplier and a second contactconnected to the second multiplier, and installed between thetransmission delay unit and the first and second multipliers, forselectively providing the signal from the first multiplier or the secondmultiplier to the transmission delay unit.

The transmission delay unit may delay the signal as long as ½n of asymbol period.

The transmission delay unit may repeat the delay of the signal 2n−1times within a symbol period.

The first and second switches may be respectively switched to theirfirst contacts for a delay time corresponding to the first ½n of thesymbol period, and may be respectively switched to their second contactsfor the remaining time of the symbol period.

The signal generator may be an impulse generator for generating animpulse signal.

The communication system may further comprises a receiver that includesa reception delay unit for receiving the signal from the transmitter anddelaying the signal as long as the delay time of the transmission delayunit, and a data judgment block for discriminating data bits of thesignal from the transmitter by comparing the signal from the transmitterwith the delayed signal from the reception delay unit.

The data judgment block may include a multiplier for multiplying thesignal from the transmitter by the delayed signal from the receptiondelay unit, and providing a plurality of signal values with respect tothe symbol period, a waveform generator for generating waveforms withrespect to the respective signal values output from the multiplier, anda data judgment unit for judging the data bits for the respective symbolperiods according to the waveforms of the respective signal valuesgenerated by the waveform generator.

The number of signal values output from the multiplier may be 2n−1 forone symbol period.

The receiver may further includes a bit judgment unit for judging thedata bits of the respective signals depending on whether the waveformsof the respective signal values generated by the waveform generatorexceed a predetermined threshold value, and providing the result ofjudgment to the data judgment unit.

The data judgment unit may judge the data bits of the symbol periodaccording to the number of data bits of the respective signal valuesincluded in one symbol period, that are judged by the bit judgment unit.

The data judgment unit may judge the data bits depending on whether asum of the respective signal values included in one symbol periodexceeds a predetermined threshold value.

According to another aspect of the present invention, there is provideda communication system having a reduced delay time, which comprises atransmitter that includes a signal generator for generating a signal fortransmitting data, a transmission delay unit for repeatedly delaying thesignal from the signal generator for a predetermined delay time within asymbol period and generating corresponding delayed signals, and aselector for selectively providing one of the delayed signals from thetransmission delay unit to an antenna; and a receiver that includes areception delay unit for receiving the signal from the transmitter anddelaying the signal as long as the delay time of the transmission delayunit, and a data judgment block for discriminating data bits of thesignal from the transmitter by comparing the signal from the transmitterwith the delayed signal from the reception delay unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects of the present invention will be moreapparent by describing certain exemplary embodiments of the presentinvention with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating the construction of aconventional DCSK type communication system;

FIGS. 2A and 2B are waveform diagrams of communication signals generatedby a conventional DCSK type transmitter;

FIG. 3 is a block diagram illustrating the construction of a DCSK typecommunication system according to an exemplary embodiment of the presentinvention;

FIGS. 4A to 4C are exemplary waveform diagrams of communication signalsgenerated by the transmitter in the case where delay times are T/4, T/6,and T/8, respectively; and

FIG. 5 is a graph illustrating simulation results of the performance ofthe DCSK type communication system according to an exemplary embodimentof the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Certain exemplary embodiments of the present invention will be describedin greater detail with reference to the accompanying drawings. In thedescription of the exemplary embodiments of the present invention, thesame drawing reference numerals are used for the same elements invarious figures. The conventional elements or their detailed descriptionwill be omitted if it is determined that they impede the subject matterof the present invention.

FIG. 3 is a block diagram illustrating the construction of a DCSK typecommunication system according an exemplary embodiment to the presentinvention.

As illustrated in FIG. 3, the communication system according to thepresent invention includes a transmitter 110 and a receiver 120.

The transmitter 110 includes a chaotic signal generator 111, a firstmultiplier 112, a transmission delay unit 115, a delay feedback loop118, a second multiplier 113, a first switch 116, and a second switch117, and carries data on a chaotic signal to transmit the data carriedon the chaotic signal to the receiver 120.

The chaotic signal generator 111, which generally uses a chaotic dynamicsystem, generates the chaotic signals having a specified characteristicfor a data transmission. This chaotic signal generator 111 generates thechaotic signals directly from frequency bands for the data transmission,such as predetermined RF signals, microwaves, infrared rays, and visiblerays.

The first multiplier 112 receives data bits of “0” or “1” for generatingdata, multiplies the data bits by the chaotic signal generated by thechaotic signal generator 111, and provides the result of multiplicationto the transmission delay unit 115. If the data bit is “0”, the chaoticsignal is inverted, and if the data bit is “1”, the chaotic signal ismaintained as it is.

The second multiplier 113 multiplies the delayed signal from thetransmission delay unit 115 by the same data bit as that of the firstmultiplier 112.

The delay feedback loop 118 adds the data bit provided from the secondmultiplier 113 to the delayed signal from the transmission delay unit115, and provides the added signal to the transmission delay unit 115again.

The transmission delay unit 115 generates a data signal by delaying thesignal generated from the first multiplier 112 as long as ½n of thesymbol period T. Here, if n is larger than 2, i.e., if n is T/4, T/6,T/8, and others, the transmission delay unit 115 alternately generates adata signal and a reference signal by delaying the signal having passedthrough the delay feedback loop 118 for ½n of the symbol period.

For example, if the delay time is T/4, the reference signal istransmitted through an antenna in the process indicated as {circlearound (1)} in FIG. 3, and the transmission delay unit 115 generates thedata signal by delaying the reference signal processed by the firstmultiplier 112 according to the data bit for T/4 in the processindicated as {circle around (2)} in FIG. 3. In this case, if the databit is “1”, the data signal generated by the transmission delay unit 115is equal to the reference signal. The generated data signal is providedto the first switch 116, and is simultaneously looped back via the delayfeedback loop 118 to the second multiplier 113 to be multiplied by thedata bit and provided again to the transmission delay unit 115, in theprocess indicated as {circle around (3)} in FIG. 3. In this case, thedata bit provided to the second multiplier 113 is equal to the data bitprovided to the first multiplier 112. The transmission delay unit 115generates the reference signal by delaying the input data signal forT/4. The generated reference signal is provided to the first switch 116,and is simultaneously provided to the transmission delay unit 115 afterbeing processed by the second multiplier 113 through the delay feedbackloop 118, in the process indicated as {circle around (4)} in FIG. 3. Thetransmission delay unit 115 generates the data signal by delaying againthe reference signal for T/4.

Accordingly, if the delay time is T/4, the reference signal provided tothe transmission delay unit 115 is converted into a data signal, and apair of the reference signal and the data signal is further generated bytwice performing the delay process through the delay feedback loop 118.That is, as illustrated in FIG. 4A, two pairs of data signals andreference signals are carried in one symbol period, and numerals markedon the respective signals indicate the signals generated through therespective processes of {circle around (1)}, {circle around (2)},{circle around (3)}, and {circle around (4)} in FIG. 3.

In the same manner, if the delay time is T/6, three pairs of datasignals and reference signals are carried in one symbol period asillustrated in FIG. 4B, and if the delay time is T/8, four pairs of datasignals and reference signals are carried in one symbol period asillustrated in FIG. 4C.

The first switch 116, which is installed between the chaotic signalgenerator 111 and the transmission delay unit 115, selects and providesone of the signals from the chaotic signal generator 111 and thetransmission delay unit 115 to the antenna. The first switch 116includes a first contact connected to the chaotic signal generator 111and a second contact connected to the transmission delay unit 115. Thefirst switch 116 is alternately switched between the first contact andthe second contact under the control of a control unit (notillustrated), and the time which the first switch 116 is switched to therespective contacts is determined according to the delay time. If thedelay time is T/4, the first switch 116 is switched to the first contactfor the first T/4 of the symbol period, and is switched to the secondcontact for the remaining amount of the symbol period. If the delay timeis T/6, the first switch 116 is switched to the first contact for thefirst T/6 of the symbol period, and then is switched to the secondcontact for the remaining symbol period. That is, the first switch 116is switched over to the first contact only for the delay time in thesymbol period, and then is switched to the second contact for theremaining time of the symbol period.

The second switch 117, which is installed between the first multiplier112 and the second multiplier 113, selectively provides the signals fromthe first multiplier 112 and the second multiplier 113 to thetransmission delay unit 115. The second switch 117 has a first contactconnected to the first multiplier 112 and the second contact connectedto the second multiplier 113. In the same manner as the first switch116, the second switch 117 is alternately switched between the firstcontact and the second contact according to the delay time. The secondswitch 117 is switched to the first contact for the delay time in thesymbol period, and provides the signal from the chaotic signal generator111 to the transmission delay unit 115, while it is switched to thesecond contact for the remaining time of the symbol period, and providesthe delayed signal from the transmission delay unit 115 to thetransmission delay unit 115 again.

On the other hand, the receiver 120 includes a reception delay unit 125,a multiplier 123, a waveform generator 127, a bit judgment unit 128, anda data judgment unit 129.

The reception delay unit 125 delays the communication signal inputthrough an antenna as long as the delay time delayed by the transmissiondelay unit 115 of the transmitter 110, i.e., for ½n of the symbol periodT. Accordingly, the delayed signal having passed through the receptiondelay unit 125 is delayed as long as ½n of the symbol period T incomparison to the signal input through the antenna.

The multiplier 123 multiplies a communication signal delayed by thereception delay unit 125 by a communication signal input through theantenna, and provides the resultant signal to the waveform generator127. At this time, the multiplier 123 multiplies the n-th referencesignal or data signal of the communication signal from the antenna bythe (n−1)-th data signal or reference signal of the communication signalfrom the reception delay unit 125. In other words, the multiplier 123multiplies 2n−1 signal pairs.

For example, if the delay time is T/4, the multiplier 123 multiplies thefirst data signal of the communication signal from the antenna by thefirst reference signal of the communication signal delayed by thereception delay unit 125, and multiplies the second reference signal ofthe communication signal from the antenna by the first data signal ofthe communication signal from the reception delay unit 125. Also, themultiplier 123 multiplies the second data signal of the communicationsignal from the antenna by the second reference signal of thecommunication signal from the reception delay unit 125. Accordingly,three signal pairs are multiplied. In the same manner, if the delay timeis T/6, five signal pairs are multiplied, and if the delay time is T/8,seven signal pairs are multiplied, respectively.

If the reference signal and the data signal are equal to each other,i.e., if the data bit is “1”, the communication signal having twice theenergy is output. If the reference signal and the data signal areopposite to each other, i.e., if the data bit is “0”, the communicationsignal having twice the negative energy is output.

The waveform generator 127 removes the chaotic signal and forms thewaveform of the communication signal by calculating averages of theresultant values of the multiplication of the signal pairs in aspecified period, for example, a symbol period, with respect to thecommunication signals output from the multiplier 123.

The bit judgment unit 128 receives the waveforms generated by thewaveform generator 127, and extracts data bits for the respective signalpairs. At this time, the data bits are judged depending on whether thewaveform is larger than a predetermined threshold value. If the waveformis larger than “0” that is the threshold value, the bit judgment unit128 judges the data bit as “1”. If the waveform is not larger than thethreshold value, the bit judgment unit 128 judges the data bit as “0”.Since the data bit is produced for each signal pair, a plurality of databits are extracted for each symbol period. For example, in the case ofthe communication signal having a delay time of T/4, three signal pairsare produced, and thus three data bits are extracted. In the case of thecommunication signal having a delay time of T/6, five data bits areextracted, and in the case of the communication signal having a delaytime of T/8, seven data bits are extracted.

The data judgment unit 129 judges the data bits of the respective symbolperiods based on the data bits of the respective signal pairs judged bythe bit judgment unit 128. That is, the data judgment unit 129 judgesthe data bits that command a majority between the data bits of “0” and“1” included in a symbol period as the data bits of the respectivesymbol periods. For example, in the case of the communication signalhaving the delay time of T/4, if the data bits of three signal pairs ina symbol period are all “1”, the data judgment unit 129 judges the databit of the corresponding symbol period as “1”. If two data bits are “1”and one data bit is “0” among the data bits of the three signal pairs,the data judgment unit 129 judges that the data bit of the correspondingsymbol period as “1”. However, if one data bit is “1” and two data bitsare “0” among the data bits of the three signal pairs, the data judgmentunit 129 judges the data bit of the corresponding symbol period as “0”.

A process of transmitting/receiving a chaotic signal in thecommunication system as constructed above in the case where the delaytime is T/4 will now be explained.

The chaotic signal generated by the chaotic signal generator 111 of thetransmitter 110 is provided to the first contact of the first switch 116and the first multiplier 112. The first switch 116 is switched to thefirst contact for T/4 of the corresponding symbol period, and thechaotic signal having passed through the first switch 116 is transmittedto the receiver 120 through the antenna as the reference signal. Afterthe delay time of T/4, the first switch 116 is switched to the secondcontact for the remaining time of the corresponding symbol period.

The chaotic signal provided to the first multiplier 112 is multiplied bythe data bit, for example, “1”, and the multiplied signal is provided tothe transmission delay unit 115. The transmission delay unit 115 delaysthe chaotic signal for T/4, i.e., the predetermined delay time. Thedelayed chaotic signal is provided to the first switch 116 and the delayfeedback loop 118, and the chaotic signal provided to the first switch116 is transmitted to the receiver 120 through the antenna.

The second multiplier 113 multiplies the chaotic signal provided by thedelay feedback loop 118 by “1”, i.e., the same data bit input to thefirst multiplier 112, and then the chaotic signal delayed for T/4 by thetransmission delay unit 115. This chaotic signal is a 2T/4-delayedsignal in comparison to the chaotic signal generated by the chaoticsignal generator 111, and is provided to the first switch 116 and thedelay feedback loop 118. In this case, the chaotic signal provided tothe first switch 120 is provided to the receiver 120 through the antennaas the reference signal.

The chaotic signal provided to the delay feedback loop 118 is multipliedby the data bit of “1” through the second multiplier 113, delayed forT/4 by the transmission delay unit 115, and then provided to the firstswitch 116. The chaotic signal provided to the first switch 116 is a3T/4-delayed signal in comparison to the chaotic signal generated by thechaotic signal generator 111, and is provided to the receiver 120through the antenna as the data signal.

If four chaotic signals, i.e., a pair of reference signals and a pair ofdata signals, are carried within one symbol, the first switch 116 isagain switched to its first contact, and the second switch 117 is alsoswitched to its first contact.

On the other hand, if the communication signal is received in thereceiver 120, the reception delay unit 125 delays the inputcommunication signal for T/4, and the multiplier 123 multiplies thecommunication signal input through the antenna by the communicationsignal delayed by the reception delay unit 125. At this time, threesignal pairs are produced by multiplying the delayed communicationsignal by the non-delayed communication signal with respect to onesymbol period. The waveform generator 127 generates the waveform byaveraging the respective signal pairs, and the bit judgment unit 128judges the data bits of the respective signal pairs. Then, the datajudgment unit 129 judges the data bit of the corresponding symbol periodusing the number of data bits of the respective signal pairs.

FIG. 5 is a graph illustrating simulation results of the performance ofthe DCSK type communication system according to the present invention.

The simulation condition is AWGN channel, 2.5 Mbps, and samplingfrequency of 16 GHz. As illustrated in FIG. 5, comparing the DCSK systemaccording to the present invention with the conventional DCSK system onthe basis of BER 10⁻³, it can be recognized that their performances arealmost the same.

As described above, according to the communication system according tothe present invention, a delay feedback loop 118 is provided, and pluralpairs of reference signals and data signals are carried in one symbolperiod through several signal delay processes performed by thetransmission delay unit 115. Accordingly, the delay time can beaccurately adjusted without the necessity of a long physical delay line,and accurate data bits can be obtained since the judgment of the databits is performed several times with respect to one symbol period in thereceiver side.

In the exemplary embodiment of the present invention, it is exemplifiedthat the bit judgment unit 128 judges the data bits for the respectivesignal pairs, and then the data judgment unit 129 judges the data bit ofthe corresponding symbol period using the number of data bits of therespective signal pairs. However, a soft decision method may be used,which judges the data bits by directly providing the waveform obtainedby averaging the respective signal pairs from the waveform generator 127to the data judgment unit 129 without installing the bit judgment unit128. In this method, the data judgment unit 129 adds the waveforms ofthe respective signal pairs, and if the sum of the waveforms is largerthan a specified threshold value of “0”, it judges the data bit as “1”,while if the sum of the waveforms is not larger than the threshold valueof “0”, it judges that the data bit as “0”.

Also, in the exemplary embodiment of the present invention, the DCSKsystem using the chaotic signal is exemplified. However, it will beapparent that the present invention can be applied to an impulse systemfor transmitting a communication signal using a pulse signal to obtainthe same effect. In the case where the present invention is applied tothe impulse system, the above-described DCSK system is prepared in thesame manner, and an impulse radio generator is used instead of thechaotic signal generator 111. In the case of applying the presentinvention to the impulse system, however, the width of the impulseshould be smaller than the delay time of the transmission delay unit115.

As described above, according to the present invention, the delay timecan be accurately adjusted even if the delay line is shortened, and thedata bits of the communication signal can be accurately judged in thereceiver side.

The foregoing exemplary embodiments and advantages are merely exemplaryand are not to be construed as limiting the present invention. Thepresent teaching can be readily applied to other types of apparatuses.Also, the description of the exemplary embodiments of the presentinvention is intended to be illustrative, and not to limit the scope ofthe claims, and many alternatives, modifications, and variations will beapparent to those skilled in the art.

1. A transmitter comprising: a signal generator which generates a signalfor transmitting data; a transmission delay unit which repeatedly delaysthe signal generated by the signal generator modified by a data bit fora predetermined delay time within a symbol period; a delay feedback loopwhich loops back a delayed signal outputted by the transmission delayunit to the transmission delay unit in order to generate a plurality ofdelayed signals; and a selector which outputs the signal generated bythe signal generator and each of the plurality of the delayed signalssequentially.
 2. The transmitter as claimed in claim 1, wherein thesignal generated by the signal generator is a chaotic signal.
 3. Thetransmitter as claimed in claim 1, wherein the selector comprises afirst switch having a first position which connects the signal generatedby the signal generator to an antenna and a second position whichconnects the signal generated by the transmission delay unit to theantenna.
 4. The transmitter as claimed in claim 3, further comprising afirst multiplier which multiplies the signal generated by the signalgenerator by the data bit that is a binary symbol of the data togenerate a data signal.
 5. The transmitter as claimed in claim 4,further comprising a second multiplier, wherein the delay feedback loopprovides the delayed signals generated by the transmission delay unit tothe second multiplier, wherein the second multiplier multiplies thedelayed signals by the same data bit as that input to the firstmultiplier.
 6. The transmitter as claimed in claim 5, further comprisinga second switch having a first position which connects the multipliedsignal generated by the first multiplier to the transmission delay unit,and a second position which connects the multiplied signals generated bythe second multiplier to the transmission delay unit.
 7. The transmitteras claimed in claim 6, wherein the transmission delay unit delays thesignal as long as ½n of a symbol period, where n is an integer.
 8. Thetransmitter as claimed in claim 7, wherein the transmission delay unitrepeatedly delays the signal 2n−1 times within the symbol period.
 9. Thetransmitter as claimed in claim 7, wherein the first and second switchesare respectively switched to their first positions for a delay timecorresponding to a first ½n of the symbol period, and are respectivelyswitched to their second positions for the remaining amount of thesymbol period.
 10. The transmitter as claimed in claim 1, wherein thesignal generated by the signal generator is an impulse signal.
 11. Acommunication system comprising: transmitter which comprises: a signalgenerator which generates a signal for transmitting data; a transmissiondelay unit which repeatedly delays the signal generated by the signalgenerator modified by a data bit for a predetermined delay time within asymbol period; a delay feedback loop which loops back a delayed signaloutputted by the transmission delay unit to the transmission delay unitin order to generate a plurality of delayed signals; and a selectorwhich outputs the signal generated by the signal generator and each ofthe plurality of the delayed signals sequentially; and a receiver whichcomprises: a reception delay unit which receives the selected signalfrom the transmitter and delays the selected signal received from thetransmitter as long as the delay time of the transmission delay unit togenerate a delayed signal; and a data discrimination unit whichdiscriminates data bits of the signal received from the transmitter bycomparing the signal received from the transmitter with the delayedsignal generated by the reception delay unit.
 12. The communicationsystem as claimed in claim 11, wherein the data discrimination unitcomprises: a multiplier which multiplies the signal received from thetransmitter by the delayed signal generated by the reception delay unit,and provides a plurality of signal values with respect to the symbolperiod; a waveform generator which generates waveforms with respect tothe respective signal values output from the multiplier; and a datajudgment unit which judges the data bits for the respective symbolperiods according to the waveforms of the respective signal valuesgenerated by the waveform generator.
 13. The communication system asclaimed in claim 12, wherein a number of signal values output from themultiplier is 2n−1 for one symbol period, where n is an integer.
 14. Thecommunication system as claimed in claim 12, wherein the receiverfurther comprises a bit judgment unit which judges the data bits of therespective signals depending on whether the waveforms of the respectivesignal values generated by the waveform generator exceed a predeterminedthreshold value, and provides a result of judgment to the data judgmentunit.
 15. The communication system as claimed in claim 14, wherein thedata judgment unit judges the data bits of the symbol period accordingto a number of data bits of the respective signal values included in onesymbol period, that are judged by the bit judgment unit.
 16. Thecommunication system as claimed in claim 12, wherein the data judgmentunit judges the data bits depending on whether a sum of the respectivesignal values included in one symbol period exceeds a predeterminedthreshold value.